New York's main contract, West Texas Intermediate (WTI) for delivery in October, was down 28 cents at USD 104.83 and Brent North Sea crude for October slipped 44 cents to USD 109.71.

The weekly report on US commercial energy stockpiles by the US Energy Information Administration is due later today and will provide an indication about the state of the world's number one economy.

The group last week said crude stockpiles shrank to 360.5 million barrels in the week to August 9, the lowest since January.

"WTI prices are looking to the US energy numbers, guidance from the Federal Open Market Committee minutes, as well as news from Jackson Hole in the coming weeks," David Lennox, resource analyst at Fat Prophets in Sydney, said.

Central bankers from around the world are set to gather for their annual get-together in Jackson Hole, Wyoming, this week. Factors driving the fall in Brent were less clear, especially given recent indications of tightness in the market as well as the lack of fresh economic data. "While news out of Europe has been optimistic, this might not have had an impact on demand yet," said Lennox.

Data last week showed that the eurozone exited its record 18-month recession in the second quarter with 0.3-percent growth.

Eyes are also on Washington, where minutes from the Fed's July policy meeting will be pored over for clues about the future of its vast stimulus programme, which has acted as a support for the economy.